Washington aware of terror threat, not afraid

The intelligence community regularly receives tips and information of this nature. But the timing of this particular threat had officials especially concerned, because it was the first "active plot" that came to light as the country marked the significant anniversary, a moment that was also significant to al-Qaida, according to information gleaned in May from Osama bin Laden's compound.

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The U.S. government has long known that terrorists see the 10th anniversary of 9/11 and other uniquely American dates as opportunities to strike. Officials have also been concerned that some may see this anniversary as an opportunity to avenge bin Laden's death.

Security worker Eric Martinez wore a pin depicting the twin towers on his lapel as he headed to work in lower Manhattan on Friday where he also worked 10 years ago when the towers came down. "If you're going to be afraid, you're just going to stay home," he said.

Mayor Michael Bloomberg, too, made a point of taking the subway to City Hall.

Briefed on the threat Friday morning, President Barack Obama instructed his security team to take "all necessary precautions," the White House said. Obama still plans to travel to New York on Sunday to mark the 10th anniversary with stops that day at the Pentagon and Shanksville, Pa.

Britain, meanwhile, warned its citizens who are traveling to the U.S. that there was a potential for new terror attacks that could include "places frequented by expatriates and foreign travelers."

Acutely aware of these factors, law enforcement around the country had already increased security measures at airports, nuclear plants, train stations and more in the weeks leading up to Sept. 11. The latest threat, potentially targeting New York or Washington, prompted an even greater security surge in those cities. U.S. embassies and consulates abroad had also boosted their vigilance in preparation for the anniversary.

At Penn Station in New York, transit authority police carried assault rifles and wore helmets and bullet-proof vests as they watched crowds of commuters. Police searched passengers' bags as they entered the subway, and National Guard troops in camouflage fatigues moved among riders, eyeing packages.

Credible, not corroborated threat

These sorts of vague descriptions are typical intelligence talk in an environment where tips come from all places and in all shapes- a stolen diplomatic cable, a satellite image showing tribesmen gathering in an area that's typically isolated, a snatched bit of conversation between two terrorists overheard by a trusted source, a phone number, a document, an email, an airplane ticket.

"Figuring out who would-be attackers are, or even whether they exist, could take months, where the drumbeat of national security wants answers in minutes or days," said Phillip Mudd, a former top counterterrorist official at the CIA and the FBI.

"You have to tell everyone what you heard, and then try to prove the information is legitimate."
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